The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus using, e.g., a rotary developing device having a plurality of developing sections and sequentially moving the developing sections to develop latent images electrostatically formed on an image carrier with developers of different colors.
Image forming apparatuses of the type described include one having a rotary developing device, or revolver as often referred to, adjoining a photoconductive drum or similar image carrier. The revolver has a plurality of developing sections arranged in preselected positions inside of a rotary body. While latent images are sequentially formed on the drum, the developing sections are sequentially moved to a preselected developing position to develop the latent images with toner of different colors. In a color image forming apparatus, for example, the developing sections of the revolver usually store black toner and toner of three complementary primary colors, i.e., cyan, magenta, and yellow, respectively.
Today, there is an increasing demand for a space-saving developing device capable of implementing a miniature image forming apparatus. The revolver is one of measures for meeting the above demand. To further save space, there has been proposed a revolver omitting tubings communicating toner cartridges each storing toner of particular color and developing sections, and positioning the cartridges in the vicinity of the developing sections. In this kind of revolver, every time the color for development is switched, the developing section storing the toner of necessary color is brought to a stop at the developing position. At the same time, the other developing sections are each brought to a stop at a particular position. The replenishment of toner from each cartridge to the associated developing section is effected via an opening provided at the portions of the cartridge and developing section joining each other. Because a single position is available for the above opening to be so oriented as not to fall the toner in the event of replacement of the cartridge, only one cartridge can be replaced at a time in the event of replenishment.
When any one of the toner cartridges runs out of toner, it is replaced with a new toner cartridge. After the replacement of the cartridge, a toner content in the developing section associated therewith must be restored to the original content, so that images can be formed with stable density even just after the replacement. A recovery operation for the restoration of the toner content is under study. For example, a discharge lamp or quenching lamp QL, a main charger, a bias for development and so forth are sequentially turned on in order to form a preselected pattern for density measurement on the photoconductive drum. The preselected pattern is read by an optical sensor for sensing density. The toner is repeatedly replenished from the toner cartridge to the developing section until an adequate toner content has been set up in the developing section. Then, the main charger, bias for development, QL and so forth are sequentially turned off, and the drum is brought to a stop. The procedure from the rotation of the drum to the formation of the density pattern will be referred to as pre-rotation processing. Also, the procedure from the formation of the density pattern to the establishment of the adequate toner content will be referred to as recovery processing. Further, the procedure from the end of the replenishment to the stop of the drum will be referred to as post-rotation processing. The pre- and post-rotation processing each needs a certain period of time because it continues until the surface of the drum reaches a stable state.
It has also been proposed to use toner sensing means for determining whether or not the toner is present in each toner cartridge either directly or indirectly, and reporting means for urging, based on the output of the sensing means, the operator to replace the cartridge needing replacement.
However, the conventional revolver has some problems yet to be solved, as follows.
Problem 1!
The revolver is so constructed as to allow only one toner cartridge located at the replacing position to be replaced. Therefore, if the cartridge reached a toner end or toner near end condition is not located at the replacing position in the event of replenishment, the operator must move the cartridge to the replacing position by hand. Particularly, it is difficult to rotate conventional revolvers by hand, so that an implementation capable of enhancing efficient replenishment is desired.
Problem 2!
Assume that the recovery operation is performed every time a cartridge is replaced. Then, the pre-rotation processing, recovery processing and post-rotation processing are repeated each time. When a plurality of cartridges are replaced, the above procedure restricts the operator to the apparatus until the replacement of the last cartridge completes, resulting in low operation efficiency. Further, such a procedure effected with a plurality of cartridges increases the overall recovery time and causes the operator to wait a long period of time up to the start of image formation. Moreover, when any one of the cartridges is replaced while a power switch provided on the apparatus is in its OFF state, which cartridge has been replaced cannot be seen when the power switch is turned on. Executing the recovery operation with all the cartridges, including even those not replaced, is wasteful. This would also causes the operator to wait a long period of time up to the start of image formation.
Problem 3!
Assume that the previously mentioned reporting means ends a report after the recovery operation has been completed. Then, because a certain period of time is necessary between the replacement of the cartridge and the end of the recovery operation, the operator is likely to inadvertently replace the cartridge associated with the same developing section twice during, e.g., recovery operation following the replacement. This is particularly true when the person replaced the cartridge leaves the apparatus, and another person uses the apparatus. Such repeated replacement simply wastes labor. In addition, it is likely that the toner existing at the portion where the cartridge and revolver join each other flies about.
Problem 4!
Assume that any one of the cartridges is absent on the revolver. Then, the rotation of the revolver is likely to cause the toner to fly about from the portion where the revolver is expected to join the above cartridge. For example, assume that the apparatus has a cover member which the operator may open and close for the replacement of the cartridge. Then, when the operator opens the cover member, the rotation of the revolver is stopped for safety operation. When the cover member is again closed, the revolver may be rotated for homing. Alternatively, while the cover member is open, the revolver may be rotated for the recovery operation. In such a case, if any cartridge is absent, the toner flies about from the above portion during the rotation of the revolver.
Problem 5!
Assume that cartridge sensing means responsive to the cartridge is located at a preselected position on a path along which the revolver moves the cartridges, and that when the operator opens the cover member for replacement, the rotation of the revolver is stopped for safety operation. Then, the cartridge sensing means is apt to operate erroneously. Specifically, it occurs that when the revolver in rotation is stopped for the safety purpose due to the opening of the cover member, no cartridges exist at the above preselected sensing position despite that all the cartridges are present on the revolver. If the revolver is stopped at such a position, the sensing means does not sense any cartridge despite that all the cartridges are present. As a result, if the apparatus operates on condition that the sensing means senses the cartridge, the apparatus will remain inoperative.
Problem 6!
The erroneous operation of the sensing means stated above also occurs when the revolver is stopped due to the turn-off of the power switch.
Problem 7!
The recovery operation is executed, based on a preselected criterion, when the cartridge is determined to have been replaced. It is likely, depending on the criterion, that the cartridge is determined to have been replaced despite that it has not been replaced, resulting in wasteful recovery operation. Specifically, assume that the cartridge is determined to have been replaced if it is in the toner end or toner near end condition when the cover member is opened and closed by the operator for replacement. Then, the recovery operation occurs even when the operator simply opens and closes the door without replacing the cartridge.